1. Field of the Invention
The present invention relates to a bioreactor carrier, a process for producing the carrier and a method for using the same. More particularly, it pertains to a bioreactor carrier which is imparted with water swelling properties, a degree of volumetric swelling or a degree of volumetric swelling along with a specific gravity, each being controlled within a specific range, and high physical strength; enables microbial reactions and enzymatic reactions to be effectively performed; and moreover is readily producible, to a process for producing the carrier in high efficiency, and to a method for effectively carrying out denitrifying treatment for organic waste water with microbes by the use of the above-stated carrier.
2. Description of the Related Arts
The carriers to be employed in bioreactors can be broadly classified into porous carriers and gel carriers. Examples of the porous carriers include those made of polyurethane, cellulose, polypropylene, polyvinyl formal, ceramic etc., respectively. Because of their being porous, the carriers have a large surface area and in the majority of cases, are employed in a state of bindingly immobilized animal cells, plant cells, microbes and/or protozoans onto the porous surfaces thereof.
However, the aforesaid porous carriers suffer from various disadvantages and drawbacks as described hereunder. Polyurethane and polypropylene porous bodies, due to their being hydrophobic, have inferior fluidity in water and moreover, make it difficult for animal cells, plant cells, microbes and/or protozoan to be bonded thereonto. Cellulose porous bodies are subject to attack by microbe, whereby their service life is unfavorably shortened. With regard to polyvinyl formal porous bodies, an industrial process for producing the same is not yet established. Ceramic porous bodies can not be fluidized in water due to their high specific gravity, thus inevitably restricting the usage.
On the other hand, there are known as gel carriers, those made of polyacrylamide, polyethylene glycol, polyvinyl alcohol and alginic acid, thermoplastic water absorbing bodies, etc., respectively {refer to Japanese Patent Application Laid-Open No. 136980/1998 (Heisei-10)}. It is a general practice to use these gel carriers by entrappingly immobilizing animal cells, plant cells, microbes and/or protozoans at the inside of the gel, and alternatively it is possible to use the aforesaid carriers by bindingly immobilizing animal cells, plant cells, microbes and/or protozoans onto the gel surfaces.
The foregoing gel carriers, which highly contain water, generally have high affinity for living matters and at the same time, impart favorable habitat to animal cells, plant cells, microbes and/or protozoans. Nevertheless, the physical strength is not necessarily sufficient in such gel carriers as those made of polyacrylamide, polyethylene glycol, polyvinyl alcohol and alginic acid, which bring about a fear of wear and collapse in the course of service in a reaction tank. In addition, the gel carriers just mentioned, when once molded into a definite shape, can not be changed to an other shape by remelting. Thus, such carriers are generally cut into a required shape in the majority of cases. In fact, the gel carriers suffer from serious disadvantages in that the step of cutting the water-containing and swollen gel into several millimeter sized regular hexahedron requires tremendous labor and period of time with the result that the production thereof becomes extremely intricate and troublesome, thus necessitating markedly long time and high cost in production.
As opposed to the foregoing, thermoplastic water absorbing gel carriers that are typified by thermoplastic water absorbing polyurethane gel carriers are well suited for use as bioreactor carriers owing to such advantages as high physical strength, capability of industrial mass production, capability of adsorbing animal cells, plant cells, microbes and/or protozoans due to their hydrophilicity without deteriorating the physiological activity thereof, favorable resistance to attack by microbes, and the like.
In these thermoplastic water absorbing gel carriers, the degree of volumetric swelling thereof is one of important characteristics. For instance, the degree of volumetric swelling, when being unreasonably low, causes deterioration in microbe adhesion due to unreasonably lowered water absorption, whereas said degree, when being unreasonably high, causes deterioration in the physical strength and/or durability, unendurabilty to practical application and the like. The degree of volumetric swelling depends upon not only the type of thermoplastic resin, but also the type and quantity of an inorganic filler to be added for the purpose of regulating the specific gravity and enhancing the adhesion of microbes to the carriers. Thus, it is extremely important from the industrial point of view to control the degree of volumetric swelling within a desirable range by a simple procedure.
In this connection, utmost importance is attached to the specific gravity of the bioreactor carriers. For instance, the specific gravity thereof, when being close to that of water on attaining steady state of adhesion, binding immobilization of microbes in a reactor, gives rise to such a problem, in the case of fluidizing the liquid to be treated in a reactor for the purpose of reaction, that the carriers are apt to move upwards and difficult to be present in the lower portion, thus causing failure to assure uniform fluidity and deteriorating the efficiency of microbe reaction.
In such circumstances, an object of the present invention is to provide a bioreactor carrier which is imparted with water swelling properties, a degree of volumetric swelling or a degree of volumetric swelling along with a specific gravity, each being controlled within a specific range, and high physical strength; enables microbial reactions and enzymatic reactions to be effectively performed; and moreover is readily producible, also to provide a process for producing the carrier, and further to provide a method for using the same.
Other objects of the present invention will be obvious from the text of this specification hereinafter disclosed.
In order to achieve the above-mentioned objects, research and investigation were intensively and extensively accumulated by the present inventors. As a result, it has been found that there is obtainable a bioreactor carrier which is imparted with the foregoing characteristics in which a degree of volumetric swelling or a degree of volumetric swelling along with a specific gravity is controlled within a specific range, by blending a water swellable thermoplastic resin such as water swellable thermoplastic polyurethane resin with a compatible resin with the aforesaid resin at the time of molding; and thereafter molding the mixed resin into a desirable form by means of an extruder, or blending the aforesaid water swellable thermoplastic resin with an inorganic filler at the time of producing the resin and/or molding the same; blending the aforesaid water swellable thermoplastic resin with said compatible resin therewith; and thereafter molding the mixed resin into a desirable form by means of an extruder. It has also been found that organic waste water can effectively be subjected to denitrification treatment by using the bioreactor carrier thus obtained as a carrier for immobilizing microbes in nitrifying and denitrifying nitrogenous components in the organic waste water. The present invention has been accomplished on the basis of such findings and information.
That is to say, the present invention provides:
(1) a bioreactor carrier (hereinafter referred to as xe2x80x9cbioreactor carrier Ixe2x80x9d) which comprises a (A) water swellable thermoplastic resin and a (B) compatible resin with the resin as the component (A), characterized in that the degree of volumetric swelling of said carrier is controlled within the range of 120 to 3000%;
(2) a bioreactor carrier (hereinafter referred to as xe2x80x9cbioreactor carrier IIxe2x80x9d) which comprises a (A) water swellable thermoplastic resin, a (B) compatible resin with the resin as the component (A), and a (C) inorganic filler, characterized in that the degree of volumetric swelling of said carrier is controlled within the range of 120 to 3000%, and that the specific gravity of said carrier on swelling in water is controlled within the range of 1.02 to 2.12;
(3) a process for producing a bioreactor carrier the degree of volumetric swelling of which is controlled within the range of 120 to 3000%, which comprises the steps of blending a water swellable thermoplastic resin with a compatible resin with the aforesaid resin; thereafter heat melting the resultant blend; extruding the molten blend through an extruder into the form of strand; and continuously cutting the strand;
(4) a process for producing a bioreactor carrier the degree of volumetric swelling of which is controlled within the range of 120 to 3000%, and the specific gravity of which on swelling in water is controlled within the range of 1.02 to 2.12, which comprises the steps of blending a water swellable thermoplastic resin with a compatible resin with the aforesaid resin and an inorganic filler; thereafter heat melting the resultant blend; extruding the molten blend through an extruder into the form of strand; and continuously cutting the strand;
(5) a process for producing a bioreactor carrier the degree of volumetric swelling of which is controlled within the range of 120 to 3000%, and the specific gravity of which on swelling in water is controlled within the range of 1.02 to 2.12, which comprises the steps of blending an inorganic filler at the time of producing a water swellable thermoplastic resin from reactants of said resin; blending the resultant blend with a compatible resin with said resin and as the case may be, an inorganic filler; thereafter heat melting the blend thus obtained; extruding the molten blend through an extruder into the form of strand; and continuously cutting the strand; and
(6) a process for denitrifying treatment of organic waste water which comprises nitrifying and denitrifying nitrogen components in the organic waste water with microbes by the use of the bioreactor carrier I or II.